摘要
水稻、小麦等一年生结实植物需要启动整个植株的衰老才能使茎鞘等营养器官的养分再调运并转运到籽粒中。由于过多施用氮肥或采用保绿时间长、抗倒性强的品种等造成的茎鞘物质运转不良，籽粒灌浆缓慢，收获时大量的可用性糖滞留在秸秆中导致收获指数降低，产量下降。我国稻麦产量高，施氮量大，在一些高产地区常有发生贪青迟熟的现象，从而减产。本研究旨在探索通过适度土壤干旱对克服稻麦贪青的作用及其机理，寻求减轻贪青危害的措施对策，为制定克服稻麦“贪青”负作用的措施和推广高产节水栽培技术提供理论依据。试验于2000-2003年在扬州大学农学院田间试验场和香港浸会大学温室进行，采用土培池和盆钵试验相结合，选用碳贮藏物质形态不同的禾谷类作物小麦、水稻为材料，设置出穗后植株体内高氮(HN)和正常氮(NN)两个水平，于花后9天进行土壤水分胁迫处理，以正常浇水为对照。分析土壤干旱诱导的衰老与碳氮同化物分配之间的关系，探明衰老与碳氮同化物再调运的控制机制。获得了如下主要结果：
1．氮肥施用过量导致稻麦贪青迟熟的不利影响，主要表现为籽粒灌浆速率和产量降低，茎鞘中滞留大量可用性糖。从花后9d起，适度土壤干旱，一方面导致稻麦植株叶片水势显著地降低，顶叶叶绿素含量下降，促进了贪青稻麦的衰老，顶叶光合速率受到干旱胁迫的抑制；另一方面，促进了茎鞘贮藏物质的运转和增加了籽粒灌浆速率。在两种氮肥水平下，土壤干旱均显著增加稻麦茎鞘碳贮藏物质对籽粒产量的贡献，与正常浇水相比，NN和HN处理小麦茎鞘贮藏水溶性糖对产量的贡献率分别提高了14.0-15.7，19.6-19.8个百分点；水稻开花前茎鞘贮藏的可用糖对产量贡献率分别提高了6.4-10.7，9.9-17.2个百分点。在正常施氮(NN)水平下，土壤干旱诱导的早衰虽然增加了籽粒灌浆速率，但由于籽粒灌浆持续期缩短太多，增加的灌浆速率不能补偿灌浆持续期缩短之所失，结果导致籽粒重和产量下降。而在高氮(HN)的情况下，适度土壤干旱提高籽粒灌浆速率之得超过了灌浆持续期缩短之失，从而使得籽粒重相对增加，产量提高，与正常浇水的对照相比小麦籽粒产量增加了17.5-20.2％；水稻的产量则提高了24.4-26.6％。这说明结实期适度土壤干旱能减轻稻麦贪青的不良影响的作用。同
王维:适度土壤干早对稻麦碳氮营养运转的调节作用及其机理
时说明一定程度土壤干早对稻麦产量的影响是正是负，与处理时期稻麦植株体内氮素
状况有密切关系。
2.氮肥和土壤水分对小麦、水稻茎中贮藏碳水化合物代谢的影响是复杂的。土壤
干旱改变了小麦茎中碳水化合物组成和碳水化合物的流向，通过诱导小麦茎节间果聚
糖外水解酶活性的上升，促进了贮藏果聚糖的降解;而水稻茎节间贮藏淀粉的降解主
要通过水解途径(a一淀粉酶、p一淀粉酶、a一葡萄糖昔酶、D一酶受到土壤干早诱导，活性
上升)而不是通过磷酸解途径(淀粉磷酸化酶受到土壤干早抑制)。适度土壤干早对稻麦
茎内蔗糖的‘饭川1e’’循环代谢(模式)有显著地影响，减弱了蔗糖代谢过程中Susy催化
的可逆途径，但却加强SPS和创V催化的单向碳流途径，使SPS在茎内蔗糖的合成中
起主导作用，明显促进了开花期喂入的贮藏’4C向蔗糖的分配，提高了茎中蔗糖的浓
度。在茎贮藏同化物快速运转期(10一30DAA)。土壤干早处理使小麦茎中蔗糖浓度较正
常浇水对照分别提高了巧.9一19.0%(NN)和34.7一40.5%(HN)，早胁迫小麦植株茎中蔗糖
浓度的提高主要来源于贮藏碳重新合成;土壤干早处理使贪青水稻茎的搪含量较正常
灌水条件下提高了10.03%(汕优63)和20.45%伊c/早)。就蔗糖代谢而言，干旱主要使
蔗糖磷酸合成酶的活性和活化状态的提高，抑制蔗糖转化酶活性，促进蔗糖合成，从
而调节整个碳水化合代谢体系，加速贮藏物质快速降解和转移。
3.贪青迟熟水稻，灌浆前期籽粒中Z+ZR、IAA和ABA的含量降低，达到峰值
的时间延迟，但灌浆后期其含量却高于正常施氮水平;GAs含量在整个灌浆期保持较
高的水平。于花后gd进行适度土壤干早处理己不影响灌浆前期籽粒中4类内源激素含
量的变化。但适度水分胁迫处理显著地促进了籽粒中ABA的累积，降低GAs的含量，
尤其是ABA与GAs的含量相对消长的变化。从花后9d，对贪青稻株施用外源ABA明
显地增加了籽粒中ABA的含量和ABA与GAs的比值，促进了茎鞘中贮藏碳水化物的
运转，提高了籽粒灌浆速率，增加了粒重，缩短了籽粒灌浆持续期，其效果与结实期
适度土壤干旱的作用是一致的。浇水掺施外源ABA，对贪青稻株的剑叶叶绿素含量及
其光合同化有着显著的影响，掺施ABA的处理在花后20d到成熟期明显诱导贪青稻株
的衰老，提高茎中SPS活性和活化状态，显著促进了稻株茎中贮藏淀粉的降解，提高
了茎中蔗糖的浓度:同时外源ABA也明显提高籽粒的库活性，促进籽粒内淀粉的累积。
水稻贪青迟熟的情况下，籽粒灌浆期适度的土壤干早可能是通过改变贪青植株籽粒中
激素代谢的平衡状态，尤其是在籽粒灌浆中后期增加籽粒中ABA与GAs的比例，增
扬州大学博士学位论文
进茎中贮藏物质向籽籽粒再运转，促进籽粒
Remobilization and transfer of the stored food in vegetative tissues to the grain in monocarpic plants such as rice and wheat require the initiation of whole plant senescence. Delayed senescence caused by either too much nitrogen fertilizer or an adoption of lodging-resistant cultivars that stay "green" too long results in much non-structural carbohydrate in the straw and leads to low harvest index. Heavy use of nitrogen fertilization, especially in highly productive areas, is well known to lead a delayed senescence. Unfavorably-delayed senescence retards the active and ordered process that partitions the photosynthetic assimilates into grams, and results in a decrease in grain weight and yield. A moderate soil drying applied at grain filling period can enhance the plant senescence and may improve the yield through remobilizing more pre-stored food to grains. In current study, the concrete container and pot experiments were conducted at Yangzhou University and Hong Kong Baptist University, from 2000 to 2003. The wheat and rice selected here was considered as different forms of stored carbohydrate in plant straw. Two cultivars of wheat or rice were grown with different N levels at initial heading in order to have variable development of senescence. A moderate soil drying was imposed from 9 d after anthesis in
consideration that the division of endosperm cell is sensitive to water deficit. The study was designed to test the hypothesis: if a soil drying is controlled properly at mid-late stage of grain filling, an early senescence induced by drought stress would accelerate the rate of grain filling by enhanced relocation of carbon stored reserves, and improved use of pre-stored C reserves may help yield where the senescence is unfavorably delayed. This research investigated the effect of drought stress on the grain filling and remobilization of stored carbohydrate in wheat and rice crops grown at heavy use of nitrogen, and evaluated that the physiological and biochemical reaction in both processes of carbon and nitrogen metabolism response to water deficit, and examined how assimilate distribution in whole plant reacted to water shortage, and determined what ABA play the role in grain filling and remobilized storage under moderate soil drying conditions. The results were shown:
1. Plant senescence was unfavorably delayed by heavy use of nitrogen, which resulted in a slow grain filling and low grain yield and more water soluble sugar (WSC) was left in straw. Water deficits treatment significantly decreased mid-day leaf potential, chlorophyll content and photosynthetic rate, and enhanced plant senescence at mid-later stage of grain filling. However, an advantaged effect that such drought stress significantly promoted remobilization of stored carbohydrate and increased grain-filling rate. When compared to well-watered treatments, the contribution ratio of remobilized carbohydrate to grain yield under water deficit conditions were respectively increased by 14.0-15.7 (NN) and 19.6-19.8(HN) percentage points in wheat, 6.4-10.7(NN) and 9.9-17.2(HN) percentage points in rice. The grain weight and grain yield under water deficit treatment were significantly decreased at NN, but significantly increased at HN. The results indicated that, at NN level, an early senescence induced by drought stress increased grain-filling rate, but severely shortened the active period of grain filling. The gain from accelerated grain-filling rate did not compensate fully for the loss caused by shortened duration, which resulted in a decrease in grain weight and yield. At HN, grain yield in wheat and rice were remarkably increased by 17.5-20.2% and 24.4-26.6%, respectively. The results showed that the gain in grain from accelerated rate of grain growth, as a result of a moderate soil drying during grain filling, could compensate fully for the loss caused by a decreased period of grain filling and
resulted in an increase in grain weight and yield in cases where plant senescence was unfavorably delayed. However, it should be empha
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